if the cylinder airmass and commanded AFR is still jumping around so will the injector pulse width.
if the cylinder airmass and commanded AFR is still jumping around so will the injector pulse width.
I count sheep in hex...
Commanded & actualOriginally Posted by smokeshow
It doesn't have to be perfect, it just needs to be done in two weeks...
A wise man once said "google it"
Ok, so here's where I'm at. In the interest of simple diagnosis, I set everything 160kpa and up to a value of 97 in the VE table. I set the boost to be about 15-20kpa higher to ensure I was pulling info entirely from the cells in that range so it was definitely constant while making sure it wouldn't go too lean. I am attaching the tune file and the log. In the log it was still exclusively BE, but I tried the same scenario with an enrichment ratio of 1.28 in the PE table to no avail.
In the log, between frames 145 and 146, the PCM reduces IDC from 48% to 41%. A single frame later, the bank 2 O2 sensor picks up the lean spike and then between frames 150-152 the wideband picks up the lean spike. This is one stand-out spike that was picked up by the scanner, but I feel it constantly while in the throttle. It seems to be isolated to bank 2 because that sensor is going nuts while this is happening.
to me it looks like the engine is misfiring badly, why is RPM decreasing and increasing like that? Even with the engine going slightly lean it shouldn't misfire like that. I'd richen everything up a bit and if it's still misfiring start looking at the fuel pressure and the engine.
I count sheep in hex...
It feels like a misfire to me too. I've spent some time ruling that out, though... First thing I did was replace all the plugs, wires are relatively new, coil packs have seen 22psi on this same engine and 850whp before on another engine. Plug gaps are on the tight side, fuel pressure is great. I've tried all sorts of fuel mixtures. The fact that the injectors actually deliver less fuel intermittently really has me scratching my head though. I have been under the impression that the jumpy engine RPM is a symptom of this fueling rather than the cause. I suppose I can check wiring and maybe try out some new coil packs.
I replaced the coil packs on bank 2, no change. I did spot some interesting stuff on the scanner during the test drive later. With the boost near 200kpa, at frame 728 the throttle does some weird stuff. Looks like ETC closing for torque management...I thought I got rid of it all though.
Wonder if this odd TPS feedback could be causing issues? Pedal was on the floor the whole time...
Not sure if it will help at all, but set BE/PE to a more constant value.
Say your desired boost level is around 195kpa. Having it set like this will prevent desired afr from moving around due to an unstable MAP reading.
Boost enrich.PNG
Yeah, I did try that. I set it to use the PE exclusively and at a static value as Chris recommended, and no change. In addition I set the VE table to a constant number past ~10psi and there was no difference.
I feel like I've tried everything on it. Nothing points a finger at why it pulls the duty cycle back. Really seems like a fuel cut torque limiter though...
Have you logged misfire?
I don't have a MAF otherwise I would. Even then I don't think its isolated to any particular cylinder, so the most information I could get out of it is that there is indeed a misfire.
Ok, so as expected, the throttle body swap had no effect. Back to the stock 78mm tb without the x-link; that's out of the equation.
I did discover something interesting when I was just fiddling around in the scanner. First I'll say that for as long as I can remember, 95% of the time I haven't been able to read DTCs or pull up the readiness statuses. Doesn't matter what vehicle, it just leaves that whole screen blank like the cable is disconnected. Hasn't really been a problem since I've never really relied on DTCs to diagnose things. Despite the blank screen, I can still clear the invisible DTCs that should be showing up. When I clear the codes with the truck running, it stumbles and sometimes dies. It does this exact thing during the first startup following a write calibration. I thought at first it might just be dealing with the lack of a MAF, setting the code, etc.. But my buddy's 2000 Trans Am exhibits this same behavior when started after writing a new tune to it, and his car still has the MAF. So that can't be it. To rule out PC software problems, he has his own cable and laptop to tune with.
My question now is, could this stumble (or whatever its cause is) be resulting with these IDC cuts under load? It feels exactly like a fuel cut torque limiter. The resemblance to another friend's traction control in his Cobra is just uncanny. Its almost like I don't have access to some critical table or setting in the tune that pulls fuel back once a certain amount of air gets in the cylinder.
if it were me i'd be checking the valve seat pressure, installed height, hydraulic lifters pumping up, battery voltage at higher RPM's, melted cat etc.
There are no extra torque tables or values in the LS1 software you are missing. If there is a fuel cut due to torque management, the InjPW = 0 during the cut.
I count sheep in hex...
I've touched on a few mechanical things in my diagnosis, but I just can't see one of those things causing IDC to drop the way it does. However I have wondered about a few other things, basically everything thats unfamiliar to the PCM. For example the 2 step, LPE 24-58 conversion harness, removed knock sensors. Can running without knock sensors cause something like this? I plan to eventually, just haven't sorted out exactly how to get the new style sensors working with the older PCM.
Ran another log on it, battery voltage is very consistent between 13.7-13.9. I will begin checking the other things you listed this weekend, Chris. Thanks.
to me it looks like the IDC drop is the result of something else going on, InjPW follows airflow. Remote diagnosis of weird problems like these is very tough, especially with a combo that is a decent way from normal. Don't rule out a bad PCM either, i've seen cases where a bad PCM will drop one of the 5V rails to some sensors at high RPM and misfire hard on one bank only, cutting spark, dropping out an O2 sensor etc. Especially if the harness is non standard and there's been any kind of shorting in the past. I've also seen rubber supercharger and turbo intake pipes suck partially or fully closed on boost take days to notice it. Good luck!
I count sheep in hex...
Just an update here... The car I mentioned initially, problem was fixed with a new set of valve springs. Valve float was definitely the main factor there.
As for my truck, I tried a different PCM and the problem persisted. So I am going to pull the engine, park my ass in the engine bay so I can inspect all the wiring and hopefully find the problem. I am using this opportunity to swap to a 6.0 and a tighter converter, so the labor isn't entirely for nothingI will update if/when I do diagnose it for certain.
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